1. Field of the Invention
The present invention relates to an ink for inkjet recording, an ink cartridge and an inkjet recording apparatus.
2. Description of the Related Art
In recent years, an inkjet recording method has become widespread since it is advantageous in terms of its simple process as an image forming method simple compared to other recording methods, easy full colorization and high-resolution image obtained even with an apparatus having a simple configuration. Such an inkjet recording method forms an image by: flying an ink by bubbles generated by heat or by a pressure generated using a piezo element; depositing it on a recording medium such as paper; and drying (or impregnate into the recording medium), and its application has been expanding to printing using printers for personal use, office use and industrial use.
Recently, there is an increasing demand for industrial use, and it has been desired to adapt to high-speed printing or various recording media. In conjunction with high-speed printing, an inkjet printer equipped with a line head has also become necessary.
Also, there is an increasing demand for an aqueous ink in view of environment and safety. However, the aqueous ink is easily affected by the recording medium, causing various problems to an image. It is particularly significant when non-smooth gloss paper is used as a recording medium.
The water-based ink requires time for drying. It is highly compatible with paper and thus has high penetrability into paper. In case of uncoated, non-smooth plain paper, penetration of the colorant into paper decreases a concentration of the colorant, which is a problem that has not arisen with a solvent-based ink.
Meanwhile, in conjunction with high-speed printing, in order to accelerate drying of an ink that has been adhered on a recording medium, a penetrating agent is added to the ink so as to have water as a solvent penetrate into the recording medium. However, incorporation of the penetrating agent in the ink increases penetrability of not only water but also the colorant into the recording medium, which is a problem of decreased image density that is different from an ink used for paint and a ball-point pen.
Also, since a color printer carries out printing by superimposing inks of various colors, namely yellow, magenta, cyan and black, there are problems with a color inkjet recording that inks as liquids are mixed with one another and that the inks flow out. Further, because of demands for high-quality printing, it has been desired to obtain not only a high-definition image having superior color reproducibility by mixing colors with less occurrences of image blurring and feathering on an ink recorded matter as a color image but also sufficiently high-definition recording even for monochrome inkjet recording using only a black ink. However, a technology with satisfactory performance has not yet been provided.
Therefore, for the purpose of improving dispersion stability of a pigment, for example, there is proposed a coated pigment obtained by binding a reactive emulsifier containing an acidic group to a pigment having a dye derivative containing a basic group on a surface thereof and then polymerizing it in the presence of an addition polymerizable monomer (see Japanese Patent (JP-B) No. 4374928).
Also, for the purpose of improving image density, there is proposed an aqueous pigment dispersion having a ratio of a specific surface area of surface-modified carbon black (m2/g)/DBP oil absorption (mL/100 g) of 0.3 to 2.5 and having a hydrophilic functional group introduced on a surface thereof (see Japanese Patent Application Laid-Open (JP-A) No. 2000-319573).
Also, there is proposed an ink having a structure that the ink includes: a resin including a colorant; and a pigment, wherein the resin including the colorant confines the colorant in a microcapsule (see JP-A No. 11-343439).
Also, there is proposed a carbon black aqueous dispersion obtained by oxidizing carbon black with ozone, wherein the dispersion has a pH of 5 to 10, and the carbon black has an average particle diameter of 10 nm to 30 nm and a DBP oil absorption of 50 cc/100 g to 180 cc/100 g (see JP-B No. 3874538).
It is said in these proposals that inks having superior high image density, scratch resistance, water resistance, marker resistance and discharge stability may be obtained, but they are not satisfactory in terms of storage stability of an ink, image density and image bleeding.
Also, to improve image density, image bleeding, storage stability and discharge stability of an ink, there is proposed an aqueous pigment dispersion including surface-modified carbon black which can be dispersed in water without a dispersant and has a value of an amount of hydrophilic functional group/specific surface area in a range of 5 μmol/m2 to 30 μmol/m2 (see JP-A No. 2000-319572). In this proposal, the surface-modified carbon black is oxidized by hypohalous acid or a salt thereof.
However, a wet oxidation process with hypohalous acid or a salt thereof is carried out in this proposal, and this requires dehydration, washing and so on, which is costly. Also, since salts and so on remains in the washing, storage stability of the ink decreases when it is used for inkjet printing. Further, it is not satisfactory in terms of image density in a case of using non-smooth paper as a recording medium.
Accordingly, it has been desired to provide an ink for inkjet recording having favorable storage stability and discharge stability of the ink, enables high image density on both smooth paper and non-smooth paper and improves image bleeding, and related technologies thereof.